The present invention concerns a valve arrangement having a valve housing which has a flowthrough passage extending between an inflow opening and an outflow opening; and having a shutoff device, for closing the flowthrough passage, which has a valve seat surrounding the flowthrough passage and a valve cone which is movable in an axial direction perpendicular to the valve seat between an open and a closed valve position and corresponds with the valve seat such that in the closed valve position, sealing surfaces on the valve cone and valve seat come into metallically sealing contact and thus close off the flowthrough passage.
Valve arrangements of this type, which are configured in particular as regulating valves, can be of various configurations depending on their application, differing in particular in terms of the embodiment of the sealing surfaces. On the one hand, the sealing surfaces can be of various forms, generally having a conical sealing surface. Embodiments are also known, however, in which the sealing surfaces rest in planar fashion against one another.
In addition, different materials are used for the sealing surfaces depending on the type of stress. For low stresses at which even soft-sealing cones can be used, the sealing edges are not particularly protected. For moderate stresses the sealing edges are stellite-coated, and for high stresses the entire contour is armored. For particularly high stresses, internal fittings can be made of ceramic, hard metal, or hardened materials.
In the context of the present invention, the term "metallically sealing" is to be understood in contrast to so-called soft-sealing arrangements, and in particular is not limited to the use of metallic materials but also encompasses arrangements in which the sealing surfaces are configured from other hard materials such as, for example, ceramic, along with so-called metallically ground seals.
In the power-generation sector in particular, or in chemical plants, it is necessary to minimize the leakage flow rate, i.e. the flow volume which passes between the valve seat and valve cone and between the valve seat and housing when the valve is closed.
In particular, it is often required that the leakage flow rate be equal to zero. This requirement often can no longer be met after an extended operating period, since the sealing surfaces are in some cases exposed to very severe stresses due to erosion, abrasion, cavitation, etc., so that it becomes necessary to rework the sealing surfaces. This represents a laborious procedure, however, and in particular can also lead to undesirable shutdowns of the facility into which they are incorporated.